A teacher demonstrated the relationship between the pressure in a gas and the volume of the gas.
Figure 12 shows the equipment used.
This is the method used.
1. Record the initial volume of gas in the syringe and the pressure reading before any weights are attached.
2. Attach a 2.0 N weight to the syringe.
3. Record the volume of the gas and the reading on the pressure gauge.
4. Repeat steps 2 and 3 until a weight of 12.0 N is attached to the syringe.
i- What was the range of force used?
[1 mark]
From ___________ N to _________ N
ANSWER
From 0 N to 12 N
Most of the students gets confused that the the range should be 2N to 12N but this is incorrect. This is because we have to notice that the recording has been made of pressure and volume before adding any weight, which means lower limit of range is 0 N (see point 1).
ii- Give one control variable in the investigation.
[1 mark]
ANSWER
Temperature of gas.
(Temperature of a gas is kept constant so that the relationship of pressure and volume can be investiated. Remember, increase ir decrease of temperature would have direct impact on both volume and pressure.
In case if you worried what is control variable have a look at the following flashcard.)
iii- When the volume of gas in the syringe was 45 cm3, the pressure gauge showed a value of 60 kPa.
Calculate the pressure in the gas when the volume of gas in the syringe was 40 cm3.
[4 marks]
SOLUTION
(You don’t need to convert P1 kPa to Pa because the required answer of P2 is in kPa.)
iv- When the volume of gas in the syringe increased, the pressure on the inside walls of the syringe decreased.
Explain why.
[3 marks]
ANSWER
As volume increases, less particles colliding with the wall per second. There will be less force on the walls of the syringe. And as per the formula P=F/A, pressure and force are directly proportional, so less force means the pressure also decreases.
